Our long-term objective is to understand the nature of all gene products involved in the various stages of infection, disease and death of mice caused by Salmonella typhimurium when the pathogen is administered by its normal oral route of entry. We also wish to understand how the genes specifying these virulence attributes are regulated in response to the eukaryotic host. In some cases, the studies will be extended to determine whether S. typhi and S. choleraesuis, which represent two Salmonella species uniquely different from the S. typhimurium-S. enteritidis group do or do not use the same genetic information for infection of cells and/or mice. Specifically, we will endeavor to: (1) define mechanisms for intestinal colonization by characterizing mutants and cloning genes, (2) analyze rates of Salmonella growth and killing in vivo, (3) enumerate and quantitate proteins synthesized by Salmonella in cells and in various in vivo environments, (4) determine mechanisms of intracellular growth and spread by isolating and characterizing mutants and cloning genes, (5) determine mechanisms for entry to and/or colonization of deep tissues by isolating and characterizing mutants with chromosomal mutations and by gene cloning, and (6) determine mechanisms for regulating Salmonella genes specifying colonization and virulence attributes in response to various environments likely to be encountered in vivo and in response to the animal host. During the course of these studies, we will be heedful of the occurrence of mutational changes that alter the ability of Salmonella to interfere with host defense mechanisms and/or to establish persistent infections since understanding the genetic control over these processes is critical for the complete elucidation of the mechanism of Salmonella pathogenicity. Our studies will make use of the technologies of microbial genetics, molecular biology, biochemistry, immunology, microscopy, and animal science. Experiments will be conducted to preclude infection of workers or in advertent release of infectious microorganisms.